This invention concerns a method and relative device to obtain in the hot state single round bars from hot single multiple elements.
The method arranges also that the single round bar obtained with this invention can be already finished in itself or may also form the starting base for producing other sections.
To be more exact, this invention concerns a method and relative device to obtain in the hot state single round bars from a single multiple element having a special multiple profile consisting of at least four single round bars and arriving on a rolling line by splitting the multiple element into its components and subjecting those components to at least one further hot rolling pass.
The single multiple element consists of a plurality of single bars placed side by side and connected together, the bars being united lengthwise along at least one of their edges.
Moreover, the method and relative device of this invention are used advantageously to obtain at least four round bars from one multiple element which contains and defines those bars.
The present applicants are aware of hot rolling methods which provide for the simultaneous hot rolling of one single multiple element containing a plurality of sections positioned side by side and connected together lengthwise so as then to split the single sections from each other still in the hot state.
These single multiple elements may be produced with a lengthwise connecting web between the single sections; in this case the connecting web has to be detached so as to separate the single sections forming the multiple element.
The state of the art covers also many devices to separate the single sections, whereby the separation is carried out by oxygen lance cutting or by means of shearing tools such as circular knives, cutters or the like.
While the first of these methods requires a subsequent step to trim the cutting zone, the second method does not ensure the required efficiency and requires a great number of tools which, besides taking up a great deal of space, need not a little maintenance.
JP-A-57-58902 discloses a method to separate the single sections forming a single multiple element, whereby the webs connecting the single sections are cooled with sprayed water before being sheared, the single sections being passed vertically into a rolling mill stand; but the method entails problems of cooling the sections and therefore cannot be applied to medium or small sections.
JP-A-60-6202 discloses a method for the hot rolling of a symmetrical multiple element consisting of two single asymmetrical sections connected by a web extending lengthwise. According to this method the splitting of the two single sections is carried out after the multiple element has been cooled. This method requires that the splitting should take place downstream of the cooling plate and not in the hot rolling line.
FR-A-750.785 too discloses a method to roll a multiple element, whereby the splitting of the single sections takes place after the multiple element has undergone a cooling step to prevent the single sections becoming curved; the splitting operation can be performed by striker tools, abrasives or by shearing. This method entails the same shortcomings and limitations as that disclosed in JP-A-60-6202.
JP-A-62-127115, JP-A-62-173020, EP-A-0199402 and JP-A-64-57907 disclose a device to split a multiple element consisting of two single sections joined together along one of their edges. The splitting devices disclosed in the above latter documents cannot be used on multiple elements consisting of more than two single sections.
JP-A-62-173001 discloses a splitting device for use on multiple elements consisting of four or even more single sections. With this device the single sections forming the multiple element have a substantially oval cross-section and are split by rotating each of the single sections about its own axis.
But this splitting device entails the problem of having to rotate these single oval sections so as to position them with their greater axis substantially vertical and to keep them in this position for the next rolling operation, by which they are shaped with a circular cross-section.
The method which employs this device requires also that the single sections, when split, should undergo at least two steps of rotation about their own axes before producing the desired single round bars; this situation entails extra costs as regards machinery and space occupied.
U.S. Pat. No. 1,977,285 discloses a method for the hot rolling of a multiple element, whereby the separation of the individual sections takes place by making the multiple element cooperate with two opposed rolls, on the surfaces of which are machined guides shaped according to the type of multiple element produced and alternately offset in relation to each other. This method can be applied to hot multiple elements leaving a rolling line and to cold multiple elements.
This teaching cannot be applied to sections rolled at high and medium-high speeds above 45-50 meters per second, since the guides have to carry out a first action of separating and steering the sections and perform very heavy work. This subjects the guides to a very great stress, which makes them unsuitable for use very quickly.
It is precisely owing to the intense work to be performed by the guides in pre-separating the single sections that the single sections are finished in the same rolling stand which completes the separation.
The state of the art includes also a method for separation in the hot state of single oval sections; this method consists in passing a multiple element into a rolling stand which subjects the single sections to rotation about their lengthwise axes and thereafter a vertical displacement as between the sections.
Next, this method requires successive passes to bring the single oval sections to the desired circular shape.
JP-A-60-92001 discloses a device to separate single bars, whereby the splitting into two separate assemblies is carried out by lateral displacement of one assembly of the single bars from the other assembly on their plane of movement. This device separates the multiple element into two assemblies at a time and therefore requires a great number of splitting devices where the multiple element consists of a great number of single bars. Moreover, the splitting elements consist of slitting rolls, which are supported on both sides, thus making the operations of maintenance and of freeing the device very complex and long.
In the device disclosed in FR-A-1,021,163 and DE-C-13,037 the single sections are separated by being moved vertically in relation to each other, this vertical movement being achieved with one or two pairs of rolls. Moreover, in the device of FR-A-1,021,163 the pairs of rolls are rotated at different speeds and are fitted within a supporting structure, thus requiring long and complex operations to free the rolls in the event of jamming and to perform normal maintenance. Moreover, the single bars, when split, are not distanced from each other and therefore cause great problems in the subsequent rolling operations.
The device disclosed in DE-A-2,612,714 includes a slitting wheel which cooperates with the web connecting two single sections forming a multiple element. The device can be used only with multiple elements consisting of two single sections, and also the slitting action performed by the slitting wheel does not enable work to be carried out at very high speeds. Moreover, the flash produced by slitting the web connecting the single sections may fall onto the cutting edges of the slitting wheel and thus may reduce the slitting power considerably and/or may fall onto the walls of the stationary separator means positioned downstream with the resulting formation of surface faults on the separated round sections.
The devices of the state of the art involve the above shortcomings and furthermore require heavy investment in the necessary rolling stands, in the space taken up by those stands and in installed and dissipated power with a resulting considerable pollution of the environment.
Moreover, if the multiple rolled element becomes jammed, the operations to free and restart the cycle with the devices of the state of the art are complicated and entail quite long times of stoppage of work.